IT must surely un-nerve some of the Royal Scottish National Orchestra’s guest conductors.

When he is not called upon to play – and bass clarinettists can have many pages of rest between one intervention and the next during rehearsals – Duncan Swindells can often be observed scribbling away behind his music stand.

But if the latest young stick-waver worries that their performance is being assessed by a critical eye in the midst of the woodwinds, the truth is that Swindells is probably somewhere else in his mind; Hong Kong perhaps, or Istanbul.

Although music is a constant thread in his family lineage, the man who has held the bass clarinet chair since the early 2000s has now started to explore the path of his parents, both published authors, with his first novel, Birth of a Spy. The first in a projected series of detective stories, its sequel is already nearing completion.

The product of Swindells’s fascination with Leo Marks, Second World War cryptographer and screenwriter of director Michael Powell’s career-sabotaging film Peeping Tom, Birth of a Spy follows unemployed Cambridge graduate Scott Hunter from a bedroom fascination with code-breaking to involvement in the murderous world of real-life espionage. While mostly set in London, its successors will take advantage of their writer’s global travels during his musical career. The urge to write, however, comes from his upbringing and parents, for whom a holiday meant an opportunity to write together.

“We used to go on family holidays and they would sit down during the two or three weeks and write, so at the end of the holiday there would be a new book," says the 49-year-old. "Then it would take two years for them to sell it to a publisher, of course, but they did have some success. Mum wrote as Drusilla Carr, which my father and I agreed was the most awful pen-name either of us had ever heard. She had quite a bit of success back in the day, with an agent selling stuff all over the world.

“She used to specialise in writing for kids who had special needs, and she also wrote for Women’s Own and that kind of thing. My dad was in advertising and wrote textbooks. Then, on holidays, the pair of them together wrote thrillers as GJ Cadbury and those did pretty well. They won the Daily Mail Book of the Year.

“I don’t know how they wrote together, and I can’t really imagine how that worked. I was only ten and I had very little interest in it at all, but I still don’t quite get it.”

As well concentrating on his own writing, Swindells is also using self-publishing to issue work by his parents that never saw the light of day, including short stories and an unpublished novel.

It was his mother’s side of the family that also carried the musical gene. “My mum’s mum was a concert pianist and her brother, my great uncle, was in the Halle, worked with Barbirolli and Sargent and joined the Philharmonia when it was started by Walter Legge in 1945. His dad and his grandfather were both trumpet players.

“I played the recorder when I was tiny and my mum would tell you that I could read music before I could read print. The clarinet was seem as the natural next step. It was either that or the oboe, and I didn’t want to play the oboe,” he says, wrinkling his nose at the very thought.

“After school I went to the Royal Academy, and worked a lot immediately. Around 2001 I met my wife, Georgia Boyd, in the Albert Hall. She’s a viola player from Tain who had been working in London, but was returning to Scotland. We did the long-distance relationship thing and then a job came up in the RSNO. I’ve been at RSNO 15 years now, which is quite a long time.

“I am going to be 50 this year and I have been playing the clarinet professionally for over 25 years. It doesn’t get any easier with time. We did a Shostakovich symphony a couple of years ago which I had not played before and it was a real struggle. To get it into the fingers takes forever, much longer now than when I was a younger man.”

Perhaps by contrast, Swindells finds that the writing comes easily, in any environment.

“I find writing a fascinating challenge and I get a real kick out of it, and it is much less stressful than playing concerts.

“I am not in a position where anyone is breathing down my neck, but I am quite methodical, so I try to write in the morning and do around 1000 words a day. But I can also write in rehearsals with stuff going on all around me, it doesn’t bother me at all. And I love it at home, when the kids are in and its bedlam.

“What I find really difficult is isolation. The orchestra was working in Inverness a while back and rather than travel I took a room to stay there and have a quiet time to write. I didn’t achieve anything at all; I just stared at the wall for hours.

“Maybe I’ll learn to appreciate peace and quiet more as time goes by, but at the moment I seem to like the chaos. I practice clarinet with the telly on, so it’s kind of the same thing.”

His own reading enthusiasms predictably include John Le Carre and Graham Greene, as well as PG Wodehouse, Paul Auster and Douglas Adams, and he is happily analytical about the inspiration for the characters in Birth of a Spy. Leo Marks, about whom he tried to film script, became the enigmatic and secretive George Wiseman.

“The character Sir John Alperton is my father really. There’s an awful lot about fathers and sons in there and he is definitely my dad in appearance. And there is a lot of me in Scott; he is also the bassoonist from a wind quintet I used to play in and a bit of somebody I knew when I was a kid who was very very bright and is a composer now.”

“Their back-story is still to come in future books. Scott discovers all about his father’s past when he is recruited into the same organisation that his dad was kicked out of.”

The second book is set in Hong Kong, Moscow and Istanbul, all places that Swindells has visited on orchestral tours. The RSNO’s most recent visit to California hasn’t featured yet.

“I don’t know how this one is going to finish, or even who is going to make it to the end. I haven’t killed anybody so far,” he muses, perhaps realising the body count in Birth of a Spy should probably be matched.

But, if a big publisher came calling, would Swindells the thriller-writer be happy to put down the bass clarinet?

“I know a lot of people my age who are now not playing, and it is strange because deep down they do miss it, but they’ve moved on to do other things in their lives. I couldn’t say that I wouldn’t miss it – I love practising actually. But I might be OK writing and practising and not doing the concerts.

“But my real worry is that if somebody said they were prepared to pay me to write, would I still be able to do it?”

Birth of a Spy, by Duncan Swindells, is available as an ebook and a paperback, priced £5.99.